The present invention relates to gear machines with improved kinmeatics, especially to gear pumps or motors, comprising two gear wheels rotatably mounted in a housing, whose gear teeth are engaged or mesh with each other and which separate a pressurized chamber and a lower pressure or outflow chamber from each other, whereby an instantaneous volume flow rate dV/d.phi..sub.1 of hydraulic medium is produced and the gear teeth meshing with each other have a transmission function or gear ratio i=d.phi..sub.1 /d.phi..sub.2.
Hydrostatic drive systems are used in many engineering fields. Displacement machines of various structural types are used for conversion of hydraulic energy. For continuous or constant pumping the gear pumps and especially the exteriorly toothed gear pumps have been most widely used. The principle reason for this is their simple structure. This leads to high efficiency and high reliability, even with difficult operating conditions, and allows economical mass production. Moreover the exteriorly toothed gear pump has the advantages of comparatively low weight and compactness because of the high energy density.
Gear machines are generally built with at least one pair of gear wheels which comprise two exteriorly toothed gear wheels (exteriorly toothed gear pump, e.g. as in FIG. 1 here) or an exteriorly and internally toothed gear wheel (internally toothed gear pump). An externally toothed gear wheel is driven and its rotary motion is translated or converted by the second exteriorly or internally toothed gear wheel. The front and rear sides of the gear teeth of the gear wheel differ according to the rotation direction. The front sides transfer the rotary motion from the driving to the driven gear wheel. In a gear pump the medium to be fed is supplied in a known way through the gear teeth gaps from the lower pressure chamber into the higher pressure or pressurized chamber. The gear teeth flanks or sides coming into engagement with each other prevent the reverse flow of the medium from the pressurized chamber into the lower pressure chamber. Since the position of engagement, i.e. the instantaneous contact point of both tooth flanks or gear teeth sides changes constantly during the engagement of the gear teeth in relation to the locally fixed housing, volume flow variations occur and, as a result, pressure fluctuations in the pressurized space or chamber occur in synchronization with the gear teeth engagement frequency.
The applications for exteriorly toothed gear pumps are frequently more limited, because of their undesirable noise properties in comparison to internally toothed gear pumps. This is particularly disadvantageously noticeable in combination with other hydraulic equipment. Besides the running noise produce by the meshing gear teeth the volume flow fluctuations called for by the periodic gear teeth engagement stimulate or excite pressure fluctuations and noise in the entire closed hydraulic system. Thus an effective reduction of its noise generation is necessary for maintaining and especially for increasing the applicability of exteriorly toothed gear pumps. A start has been made by definite reduction of the volume flow pulsations occurring in operation. Suitable experiments in past years utilize parameter optimization of involute gear teeth and lead to solutions such as the introduction of play-free gear toothing or use of two gear wheel pairs displaced relative to each other in a Duo-pump.
As constant as possible volume flow rate is provided for noise reduction in gear pumps described in German Patent Document DE 4022500 A1, U.S. Pat. No. 5,639,230 and in European Patent Document EP 0539396 B1. The instantaneous volume flow rate, dV/d.phi..sub.1 of hydraulic medium of the gear pump or gear motor is given by the following general formula I: ##EQU1## wherein .phi..sub.1 and .phi..sub.2 are the angular positions of the driving and driven gear wheels respectively, r.sub.a1 and r.sub.a2 are the crown circle radii of the driving and driven gear wheels respectively, b is the gear tooth width of the gear teeth of gear wheels 1 and 2 respectively, and i=d.phi..sub.1 /d.phi..sub.2, the transmission function or gear ratio between the driving gear wheel 1 and the driven gear wheel 2, r.sub.w1 is the drive wheel radius of the driving wheel 1 and g.sub..alpha.y is the spacing of the instantaneous contact point Y from the pitch point C. The spacing g.sub..alpha.y depends on the angular position .phi..sub.1 of the driving wheel.
If one substitutes the relationship between the drive wheel radius r.sub.w1 and the center distance a.sub.w between the gear wheels in the formula I above for the instantaneous volume flow rate, one obtains the following formula II of the instantaneous volume flow rate ##EQU2##
The crown circle radii r.sub.a1 and r.sub.a2, the gear tooth width b and the center distance a.sub.w between the gear wheels in this formula II are geometric variables describing the gear structure. The spacing gay is the spacing of the instantaneous contact point Y from the pitch point C fluctuates between two extreme values in synchronization with the gear teeth engagement frequency. In order to compensate for the volume flow fluctuations the gear teeth should be designed according to the disclosure in German Patent Document DE 4022500 A1 and in European Patent Document EP 0539396 B1 so that the dependence of the remaining variable, namely the transmission function i, during the engagement of the gear teeth according to the spacing g.sub..alpha.y is set or determined so that the resulting volume flow rate fluctuations are null or zero. This is accomplished by setting equation II above constant.
However difficulties can result during actual operation with the gear teeth shape calculated with these relationships. The resulting gear teeth flank or side geometry leads to a transmission behavior with this special gear wheel teeth structure which has a discontinuity at the gear tooth engagement change point. This has the consequence that the angular acceleration of the driven gear wheel instantly and discontinuously changes from a positive to a negative value. The occurring force change, especially unloading, at the contact point of the gear teeth sides can have a negative effect on the feed behavior and the noise behavior of the gear device at predetermined operating points.